Ask for advice on the problem of switching power supply, novice, hehe

The switching power supply is to achieve the purpose of voltage stabilization by detecting the output voltage and sampling the pulse width or frequency of the switch tube through optocoupler, etc., the switching power supply is working in a high-frequency state, the capacity of the electrolytic capacitor is very large, the charging speed is fast, and the shutdown time is very short, so the voltage drop of the capacitor during the shutdown period is very low, that is, the output wave voltage is generally very small, only tens to hundreds of millivolts.

Another official name for switching power supply is "DC pulse power supply". It outputs a (high-frequency) pulsating DC current, so the output of the power supply only needs one diode to "pulse" and "DC" (note that it is not 'rectification' as mentioned in some books, it is completely different from the concept of rectification). The difference between a stable DC pulse and a DC pulse is only whether there is a capacitor or not at the power supply end for "energy storage".

Since the frequency of the power pulse is much higher than that of the power frequency pulsating DC, reaching thousands to tens of kilohertz, this filter capacitor is smaller than the filter capacitor of the power frequency current, but its effect is much greater. The output voltage of the switching power supply is maintained by this capacitor. From a theoretical point of view, the voltage at the capacitor (source) end will drop when the square wave pulse is cutoff, but in fact, because it has a high frequency, and due to the support of the characteristic of "the terminal voltage of the capacitor can not be abruptly changed", the second pulse wave does not wait for its voltage to drop and the second pulse wave comes up again, so the switching power supply can output a stable DC voltage under the energy storage effect of the filter capacitor.

It is recommended that the landlord take a look at the principle of the oscillation circuit.

<> visible voltage output is in the form of half-wave rectification, because the frequency of this AC power supply is much higher than the power frequency, so when using capacitor filtering, it can not only be electrolytic capacitors, but also need to be convenient to filter out high-frequency small capacitors, such as the porcelain capacitor you add to try; Because electrolytic capacitors exhibit inductance characteristics at high frequencies, this is probably the reason for your doubts;

Problems in either area will cause the output voltage to rise. Maintenance method: Due to the overvoltage protection circuit in the switching power supply, the output voltage is too high and the overvoltage protection circuit will first act. So for the repair of this fault, we can do it by disconnecting.

As long as the power of the switching power supply can meet the load demand, it cannot be blindly increased. Generally speaking, when the load of the switching power supply reaches more than 80%, the efficiency is the highest and the loss is the smallest. Therefore, the efficiency of the switching power supply with excessive power is actually used.

The thinking is more confusing, so I'll help you sort it out first.

1。First of all, you need to make it clear that the main energy transferred by the switching power supply through the transformer, not the voltage, the reason why the problem is usually described in terms of voltage is because the final measurement and comparison is the voltage value.

2。The waveform output by the transformer without rectification filtering is definitely not constant voltage, and even after rectification filtering, it is already a sawtooth wave that is close to constant voltage.

3。During the time period when the switch tube is turned on, the main thing is to charge the primary inductor, which is long, and the primary charging time is long, so that the transformer stores more energy, and then the secondary output energy is more, and the voltage is high under the same load. So again, as the question says, it is the energy that regulates the voltage.

4。The adjustment process is a dynamic and continuous process, which is why the output is a sawtooth wave.

I don't think you can fully understand what I'm talking about, and most of what you're saying is probably what others tell you or what you read in books. There are also some things that you don't have to understand at the beginning, others will remember their experience after telling you about it, and you can gradually understand it through slow accumulation, so that you can form your own experience.

The point is, you see the system as ideal. The transformer has internal resistance, the load is large, the current is large, and the load voltage will fall.

The output of the switching power supply is a valid value after filtering, the voltage rises when it is turned on, and the voltage decreases when it is turned off, which is the switching ripple (the frequency is large, and this ripple cannot be seen). When the load is large, the voltage that falls down is more during the same shutdown time, so the effective value is low. It is also necessary to consider the losses such as transformer internal resistance and coupling.

There are 2 main considerations for you:

1。Transformers have losses such as internal resistance.

2。The input voltage is fluctuating, not ideal DC, and the stable output voltage DC is fluctuating. is a valid value!

First, about how to adjust the output voltage by controlling the ratio of the switch tube on and off, it can be explained by power conservation and volt-second value balance, which is the core problem of switching power supply, it is recommended that you find a professional switching power supply book to take a look, you can understand it more thoroughly, three words can not help you fully understand the working principle of switching power supply.

Second, the output power supply of the switching power supply is never an absolute constant voltage, and there is a small amount of ripple and noise on the basis of the constant voltage.

Third, the output end of the power supply will add a capacitor, the voltage on the capacitor can not be abrupt, and the switching speed of the switch is very fast, so the voltage will never drop to zero.

The current and voltage are realized by controlling the self-controlled duty cycle, of course, this is the DAO for the zhi switching power supply with fixed frequency pulse width modulation. If it is not a fixed-frequency pulse-width modulation, changes in output voltage and current will cause changes in frequency and duty cycle.

No matter what kind of switching power supply it is, the duty cycle is close to zero at no load, and the high and low duty cycle of the voltage does not change much. The duty cycle increases as the load increases. Generally, the maximum duty cycle of the flyback switching power supply is less than 50%, which is determined according to the input voltage, the required output voltage and the maximum output current, and the relationship between the voltage and current in the work and the duty cycle does not need to be cared about.

The switching step-up and stabilized power supply connection control mode is generally divided into two types: width modulation type and frequency modulation type.

In practical applications, the widening type is used more. Specifically, you can check the circuit diagram used by yourself.

The output current of the switching power supply (fixed voltage) is related to the duty cycle of the switch, the larger the load, the larger the duty cycle, the smaller the current, which is the principle that the switching power source can stabilize the output voltage. Are you wrong or misunderstood, the principle of regulated power supply and charger is also like this, what is changed is the size of the duty cycle, to change the size of the current, in order to obtain the stability of the voltage. As for the power frequency, this parameter is generally fixed, China's existing power supply frequency is 50Hz, and the power supply frequency of some countries in the world is 60Hz, of course, the power supply of these two frequencies can be connected to the grid through frequency conversion equipment.

The duty cycle is close to zero when there is no load, and the duty cycle of the voltage does not change much. The exclusive duty ratio increases with the weight of the load. Generally, the maximum duty cycle of the flyback switching power supply is less than 50%, which is determined according to the input voltage, the required output voltage and the maximum output current.

The principle of switching power supply that can boost the voltage is exactly the same as that of the ordinary transformer step-up, and the step-up lies in the transformer with a small number of primary turns and a large number of secondary turns, which has nothing to do with whether it works in the [switch] state.

Regulated switching power supply, change the frequency or change the duty cycle, you can change the output voltage, but in practice, as long as you change the same, in practice, the switching power supply powered by the charger, color TV, and electronic circuit board --- change the duty cycle to the fundamental output voltage.

Rectangular pulse duty cycle], which can be understood by mechanical switch simulation:

A DC power supply, the positive pole is connected to the DC motor through a switch, the other end is connected to the negative pole of the power supply, and a large capacitor and a voltmeter are connected in parallel at both ends of the load. When the switch is closed, the motor is working normally after the capacitor is fully charged.

At this time, if the DC supply voltage fluctuates unsteadily, or the load of the DC motor changes, the voltage will fluctuate. In order to fix the voltage [voltage stabilization] and then stabilize the motor speed, it is necessary to use the motor of the [voltage fluctuation bottom line], such as the power supply of 10 volts using a 5 volt motor, and then use the repeated [same, off] switch to control the motor voltage to 5 volts, the operator of the on, off switch, to always monitor the motor parallel voltmeter, when the voltage is high, disconnect the switch, when the voltage is low, to stabilize the motor power supply voltage with the length of time of [on] and [off], open for a while, the output voltage is high, If the voltage is low for a while--- the ratio of time between [on] and [off] is called [on, off duty cycle]. Because the motor has a large capacitor in parallel, the motor voltage is not 0-10 volts, but fluctuates around 5 volts, if the switching speed is very high and can almost be synchronously compensated with the voltage fluctuation, it can be considered that the motor power supply is regulated.

In order to stabilize the voltage to the normal working range of the electrical appliances, the electronic components are used as switches, the electronic components operate the electronic switch, and the electronic components are used for voltage monitoring, and the electronic components are used for voltage change [sampling], and the electronic components are used for voltage overcurrent protection as backing protection--- which constitutes a complete switching power supply.

For details of the specific principle, please refer to [Switching Power Supply Circuit Diagram]--

Generally, the maximum proportion of flyback switching power supply is less than 50%, which is determined according to the input voltage, the required output voltage and the maximum output current, and the relationship between the voltage and current in the work and the proportion does not need to be cared about. No matter what kind of switching power supply it is, the duty cycle is close to zero at no load, and the duty cycle of the voltage does not change much.

No, there is a switching copy power supply with width modulation, there is a switching power supply with frequency modulation, you can find a buck circuit zhi to see its working principle about the price reduction principle, you can see the working principle of the boest circuit about the boost circuit, you can look at the buck-boest circuit about the buck-boost circuit, you can find a book on the switching power supply to view the principle.

Love is too crazybai 2013-8-10 23:49

The main reasons for the poor load energy of the switching power supply are: zhi1, all of the pre-DAO and post-stage.

Whether the capacity of the filter capacitance is at the normal value (the capacity of the pre-filter capacitor is insufficient, which will cause the power supply to have a chirping sound), 2. Whether the power supply is overloaded, 3. The oscillating negative feedback capacitor (the capacitor capacity is reduced) is easy to cause the power supply to decrease the load capacity or power supply to stop vibration. The quality of capacitors is sometimes not detectable with a multimeter. It is recommended to use the substitution method to row them one by one.

Suppose that switch (three bai

The DU has been disconnected for a long time, and all the components are in the DAO

Ideally, capacitive voltage.

Specifically equal to the input voltage. The following is divided into two parts: charging and discharging to illustrate this circuit.

Charging process. During the charging process, the switch is closed (triode on), the equivalent circuit is shown in Figure 2, and the switch (triode) is replaced by a wire. In this case, the input voltage flows through the inductor. The diode prevents the capacitor from discharging to ground.

Since the input is DC, the current on the inductor increases linearly at a certain ratio, which is related to the size of the inductance. As the current of the inductor increases, some energy is stored in the inductor.

The switching power supply is to use the circuit control switch to carry out high-speed communication and cut-off direct current.

The high-frequency alternating current is supplied to the transformer voltage converter for voltage transformation, thus generating one or more sets of voltage required! The reason for switching to high-frequency AC is that the efficiency of high-frequency AC in the transformer transformer circuit is much higher than that of 50Hz, so the switching transformer can be very small, and it is not very hot when working! The cost is low

The working principle of a switching power supply is:

1.The AC power input is rectified and filtered to DC;

2.The switch is controlled by a high-frequency PWM (pulse width modulation) signal, and the DC is added to the primary of the switching transformer;

3.The switching transformer induces a high-frequency voltage and supplies the load through rectifier filtering;

4.The output part is fed back to the control circuit through a certain circuit to control the PWM duty cycle to achieve the purpose of stable output.

When the AC power is input, it generally has to pass through something like the ehrosphere to filter out the interference on the power grid, and also filter out the interference of the power supply to the power grid;

When the power is the same, the higher the switching frequency, the smaller the volume of the switching transformer, but the higher the requirements for the switching tube;

The secondary stage of the switching transformer can have multiple windings or one winding with multiple taps to get the required output;

Generally, some protection circuits should be added, such as no-load, short circuit and other protection, otherwise the switching power supply may be burned.

Hello, this is a voltage regulator circuit. After zooming in, for high-frequency AC interference signals, the Y capacitor is equivalent to the positive or negative pole on the high-voltage DC side, so there is no problem.

It doesn't matter, it's all the same, for high-frequency AC interference signals, the Y capacitor is equivalent to the positive or negative pole connected to the high-voltage DC side.

This is a regulated circuit. Through bridge rectification and automatic voltage regulation. Power supply to the power supply.

Normally, there are two filters after rectification. Most of the capacitors used in large quantities are electrolytic capacitors. After passing through the automatic voltage regulation circuit, the output should also have a voltage regulator capacitor.

This capacitor is also an electrolytic capacitor with positive and negative poles. From here, there are two power lines, and the positive pole of the electrolytic capacitor is the positive pole of the power supply. The negative pole of the electrolytic power supply leads out the wire, which is the negative pole wire, also called the ground wire.